1. Field of the Invention
The present invention relates to a solid-state imaging apparatus, and, more specifically, to a linear image sensor having a pixel array in which a plurality of receiving elements are disposed along a charge transfer direction and of which a plurality of CCD registers are arranged on each side.
2. Description of Related Art
A linear image sensor transfers a signal charge which is stored in a light receiving element such as a photodiode via a CCD (Charge Coupled Device) register and outputs the signal charge which is converted to a voltage. The linear image sensor which has CCD registers arranged on each side of a photodiode (pixel) array is often used, because it is easy to be designed. The Staggered structure is also often used. The Staggered structure has a plurality of pixel arrays which is shifted by ½, ⅓, ¼ . . . pixel pitches. By having such a structure, the liner image sensor can be high-resolution.
As described above, the solid-state imaging apparatus which has CCD registers arranged on each side of the photodiode array is disclosed in Japanese Unexamined Patent Application Publication No. 2-91954 (Hirama). The solid-state imaging apparatus by Hirama discloses a structure in which each of the CCD registers is connected to the floating diffusion. However, when each of the CCD registers has an output circuit, the solid-state imaging apparatus needs to have two output circuits. Therefore, there is a problem that the area of the solid-state imaging apparatus increases.
To overcome the above problem, another solid-state imaging apparatus is disclosed by Hirama that two rows of the CCD registers are joined by folding back the edge on the same side of two rows of the CCD registers by 90 degrees. Then the joined CCD register is connected to a single floating diffusion. The floating diffusion converts the signal charge output from the joined CCD register into a voltage. In this case, as the CCD register is folded back by 90 degrees, it is difficult to layout design of the CCD register. Further, transfer efficiency of the signal charge input to the CCD register is easy to worsen. In another solid-state imaging apparatus, two rows of the CCD registers are approximated little by little. Then the junction of the joined CCD register is connected to a single floating diffusion.
FIG. 7 shows a solid-state imaging apparatus approximating the two rows of the CCD registers little by little, and connecting the joined CCD register to a single floating diffusion at the junction of the joined CCD register. As shown in FIG. 7, a solid-state imaging apparatus 90 has a photodiode array 91 including a light receiving element such as a plurality of photodiodes or the like, a CCD register 92, a CCD register 93, a floating diffusion 94, a reset transistor 95, an output circuit 96, and constant-voltage sources 91 to 93. The CCD register 92 and the CCD register 93 are joined at the end of the charge transfer direction. The output circuit 96 and the floating diffusion 94 are connected to a metal wiring 97. The floating diffusion 94 is connected to the reset transistor 95. In the solid-state imaging apparatus 90, the signal charge which is output from the CCD register 92 and the CCD register 93 is converted to the voltage at the floating diffusion 94, and the voltage is output from the output circuit 96 via the metal wiring 97.
Another solid-state imaging apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 7-46371 (Akiyama). The solid-state imaging apparatus includes one or two output circuit(s). Then the output circuit outputs the voltage in accordance with the charge which is output from two rows of the CCD registers. That is, the solid-state imaging apparatus by Akiyama inputs the charge transferred by each CCD register into the charge composition portion, and a single output circuit connected to the charge composition portion outputs the voltage in accordance with signal charge. Otherwise the charge transferred by each CCD register is output from the output circuit connected to each CCD register.
However, in the solid-state imaging apparatus by Hirama which approximates two rows of the CCD registers little by little and outputs the signal charge from the single floating diffusion, the number of elements of the CCD register increases, and the area of the solid-state imaging apparatus increases. The reason is as follows. For example, when a photodiode disposed between the CCD register 92 and the CCD register 93 is large, the distance of the CCD register 92 and the CCD register 93 is long. In such a case, the CCD registers of two rows are approximated little by little, and the CCD registers of two rows are joined. The number of elements of the CCD register thereby increases. When the distance of two rows of the CCD registers is long, it needs a plurality of electrodes of the CCD register by approximating two rows of the CCD registers little by little for improvement in the ability of the transfer efficiency of the signal charge. That is, the area of the solid-state imaging apparatus increases. In the solid-state imaging apparatus disclosed in Akiyama, when two rows of the CCD registers are joined, a plurality of the elements of the CCD register are needed to be disposed and the area of the solid-state imaging apparatus increases like the technique by Hirama. When two rows of each CCD register outputs the signal charge, the area of the solid-state imaging apparatus increases because each CCD register has an output circuit.